1. Technical Field
The present invention relates to a driving method of an electrophoretic display device, an electrophoretic display device, and an electronic apparatus.
2. Related Art
JP-A-2003-84314 discloses an electrophoretic display device in which a plurality of microcapsules is interposed between a pair of substrates. In this kind of electrophoretic display device, a first substrate on which pixel electrodes are formed is adhered to a second substrate provided with an electrophoretic element in which the plurality of microcapsules is formed so that the electrophoretic element is interposed between the first and second substrates.
However, the above-mentioned microcapsule-type electrophoretic display device has a problem in that “color fade-out” or “display blur” occurs after displaying an image. In particular, the color fade-out at the border between white and black outstandingly appears. Hereinafter, a phenomenon causing the color fade-out will be described with reference to FIGS. 21A to 21C.
FIG. 21A shows a microcapsule-type electrophoretic display device and FIGS. 21B and 21C show two adjacent pixels of the electrophoretic display device of FIG. 21A in an enlarged view.
The electrophoretic display device shown in FIG. 21A includes a first substrate 30, a second substrate 31, and an electrophoretic element 32 in which a plurality of microcapsules 20 is arranged and which is interposed between the first substrate 30 and the second substrate 31. A plurality of pixel electrodes 35 is arranged on the electrophoretic element 32 side of the first substrate 30. On the other hand, a common electrode 37 which opposes to the plurality of pixel electrodes 35 is formed on one surface of the second substrate 31, and the electrophoretic element 32 composed of the plurality of microcapsules 20 is provided on the common electrode 37. The electrophoretic element 32 and the first substrate 30 are adhered to each other via an adhesive layer 33.
Details about each of members of the electrophoretic display device will be described with reference to FIG. 2 in the following description.
FIG. 21B shows a state of the electrophoretic display state after an image is displayed by applying a predetermined voltage between the pixel electrodes 35 and the common electrode 37 in the electrophoretic display device having the above-mentioned structure. In FIG. 21B, a pixel electrodes 35a is applied with a negative voltage, for example −10V, and a pixel electrode 35b is applied with a positive voltage (for example, 10V). The common electrode 37 has a ground potential 0V. In a microcapsule 20a provided on the pixel electrode 35a, black particles 26 charged positive are drawn to the pixel electrode 35a side and white particles 27 charged negative are drawn to the common electrode 37 (a white display). In a microcapsule 20b provided on the pixel electrode 35b, white particles 27 charged negative are drawn to the pixel electrode 35b side and black particles 26 charged positive are drawn to the common electrode 37 (a black display).
In the electrophoretic display device, after the image display operation shown in FIG. 21B, a display is maintained by the memory characteristic of the electrophoretic element 32. Accordingly, as shown in FIG. 21C, each of the pixel electrodes falls into a high impedance state (an electrically disconnected state).
However, although each of the pixel electrodes is in the high impedance state, it is difficult to continuously and perfectly maintain the display. That the color fade-out occurs as time passes.
It is assumed that the followings comprehensively affect the color fade-out phenomenon.
First of all, the adhesive layer 33 and the shell (wall film) of the microcapsule 20 which fix the microcapsules 20 to the surface of the pixel electrodes 35a and 35b become leakage paths and therefore leakage current between the pixel electrodes easily occurs. Further, this is because the adhesive layer and the wall films must not have high resistance because it is needed to effectively apply a voltage to the microcapsule 20.
In particular, a gap between the pixel electrodes 35a and 35b has a small value of about several μms to several tens of μms so as to respond to a high definition display. Accordingly, after each of the pixel electrodes falls into the high impedance state, charges applied to the pixel electrodes 35a and 35b beforehand may come to move between the pixel electrodes 35 via the adhesive layer 33 or the wall films of the microcapsules 20. In the case of having a structure in which a switching element, such as a selection transistor, is provided for each of the pixels, off current (off leak) of the transistor becomes one of the leak paths.
Owing to the migration of the above-mentioned charges, all of the pixel electrodes 35 become the same potential (convergence potential Vc). For example, as shown in FIG. 21C, a positive convergence voltage +Vc is applied to the pixel electrodes 35a and 35b. With this operation, electric field which is opposite to electric field generated in an image writing period is applied to the microcapsule 20a disposed on the pixel electrode 35a by which the white display is performed. As a result, as shown in the figure, some of the black particle 26 and some of the white particles 27 electrophoretically migrate and therefore a display state changes (color fad-out occurs). Further, when the pixel electrodes 35a and 35b have a negative convergence potential, such color fade-out occurs in the black display pixel.
In the known electrophoretic display device, the image display state changes after the image display due to the above operation and therefore the color fade-out occurs.